Method of assembling an image intensifier



Dec. 22, 1970 J, MOEGENBlER I 3,549,229

METHOD OF ASSEMBLING AN IMAGE INTENSIFIER Original Filed Sept. 15, 1967mumm- 3| Inventor 65 5 Joseph Moegenbler %M a/ ig Nirrogen\ UnitedStates Patent 3,549,229 METHOD OF ASSEMBLING AN IMAGE INTENSIFIER JosefMoegenbier, Morton Grove, Ill., assignor to Zenith Radio Corporation,Chicago, 111., a corporation of Delaware Original application Sept. 15,1967, Ser. No. 669,470, now Patent No. 3,515,924, dated June 2, 1970.Divided and this application Nov. 13, 1969, Ser. No. 876,424 Int. Cl.H01j 9/38, 17/26 US. Cl. 316-21 10 Claims ABSTRACT OF THE DISCLOSURE Theenvelope of the image intensifier is principally a glass cylinder closedat one end to support the viewing screen and having a sealing land atthe other end with a series of apertures spaced thereabout. This end ofthe envelope is closed by a glass cap secured to the sealing land by aglass to glass seal. The photocathode has a sup-' porting framedimensioned to be positioned within the principal envelope section andhaving threaded mounting bushings in radial alignment with the aperturesin the sealing land of the envelope, respectively. Mounting pinsinserted through the openings of the envelope thread into these bushingsand mechanically secure the photocathode in position. Each pin is sealedto the envelope in a vacuum-tight seal.

In manufacturing the image intensifier three tubulations are aflixed tothe envelope, being spaced about the viewing screen thereof, and afixture having three tines is inserted through these tubulations intothe envelope and advanced toward the sealing land. The pickup pack isrested on the ends of these tines and the fixture is then withdrawn todraw the pickup pack away from the sealing land where it remains untilthe cap is sealed to the principal envelope section. Thereafter, thefixture is advanced once more to bring the mounting bushings of thepickup pack into alignment with the apertures on the sealing land forthe purpose of receiving the mounting pins.

CROSS-REFERENCE TO RELATED APPLICATION This application is a division ofapplication Ser. No. 669,470, filed Sept. 15, 1967, and assigned to thesame assignee as the present application.

Background of the invention Image intensifiers are now quite well knownand are used, for example, to obtain X-ray images while subjecting apatient to a minimal radiation dosage. Usually, they comprise anenvelope which is transparent to X-radiation in order to admit an X-rayimage to a pickup pack. This pack, in response to an incident X-rayimage, develops an electron image which is focused and acceleratedtoward a viewing screen at the opposite closure of the envelope. At thatscreen, the electron image is converted into a light image. Since theintensifier exhibits high sensitivity to X- radiation, the dosagerequired to obtain the X-ray picture from a patient is greatly'reduced.

As made heretofore, the envelope structure has a principal cylindricalsection that terminated in a metallic sealing flange which wasdimensioned and configured to match a similar flange provided on theclosure cap of the envelope. It was common practice to install thecomponents of the intensifier while the envelope sections wereseparated, and then to integrate them into a single unit by welding thesealing flanges. Although this has permitted the manufacture ofacceptable devices, it has been subject to certain disadvantages. It hasbeen found, for example, that the metal to metal seal of the envelopesections could give rise to leaks which would destroy the requiredvacuum. It has also been found that the metal flange sections of theenvelope present diflicult outgassing problems. And, finally, this is amore expensive structure than on utilizing simply glass envelope pieces.

On approach to an all-glass intensifier has been proposed in which theprincipal envelope section includes the pickup pack which may beinstalled before the envelope has been completed. The cap or end sectionto be sealed to the principal envelope piece contains the final viewingscreen. Forming an intensifier with this sort of envelope presentsdifiiculties in establishing or completing the electrode system.Usually, the electrodes take the form of conductive coatings depositedon the inner walls of the envelope and such a deposit is apt to bedestroyed and a poor glass to glass seal made if it has been put inplace before the envelope sections are sealed together, at least insofaras concerns a conductive coating in the immediate vicinity of the seal.Accordingly, it has been necessary to try to enter the completedenvelope through the exhaust tubulation or similar port and complete theelectrode system after having sealed the envelope pieces together. Thisleads to cumbersome and diflicult processing.

Summary of the invention Accordingly, it is an object of the inventionto provide a novel image intensifier as well as a novel method of itsmanufacture.

It is a further object of the invention to provide a novel andsimplified method of manufacturing an image intensifier having anall-glass envelope.

It is still another object of the invention to provide an imageintensifier that is unique in its overall structure and in particularcomponent parts.

An image intensifier embodying the invention comprises an envelopesection having a sealing land at one end and having a plurality ofapertures spaced thereabout. Another envelope section, which like thefirst is preferably formed of glass, is sealed to the land of the firstsection. The photocathode is disposed transversely of the first envelopesection and has a supporting frame with maximum dimensions less than theinternal dimensions of the first envelope section. The photocathodeframe further has a plurality of mounting provisions arranged in radialalignment with the apertures of the sealing land of the en velope. Aplurality of mounting pins individually project through one of theenvelope apertures so that one end thereof is received in couplingengagement with the mounting provisions of the photocathode frame whilethe other end is sealed to the envelope in a vacuum-tight manner.

The anode subassembly of the image intensifier to be disclosed is alsounique. It incorporates the anode electrode and phosphor viewing screenin a structural arrangement by which the subassembly is snap-locked to agroove provided on the output window of the image intensifier. Thisarrangement reduces light feedback from the viewing screen which ishighly desirable.

Another desired innovation of the intensifier is the formation of chromeoxide on the inner periphery of the envelope section which intervenesthe final focusing electrode and the anode. This is a very highresistance coating with good mechanical properties which obviates theaccumulation of charged effects on this portion of the envelope that mayotherwise be encountered if this envelope section is permitted to beleft bare.

Also, in accordance with the invention, such an image intensifier isassembled by inserting a transverse component, such as its pickup .pack,in the open end of the one principal envelope piece but is displacedfrom the sealing 3 land and the apertures thereof in the direction ofthe opposite end of the envelope. A second envelope piece is then sealedto the sealing land of the first-mentioned piece;

Thereafter, the pickup pack isadvanced toward the seal and positioned sothat its mounting provisions are in radial alignment with the aperturesprovided in the sealing land of the envelope. Then, mounting pins areinserted through these apertures into coupling engagement with themounting provisions of the pickup pack and a vacuumtight seal is madefor each such mounting pin where it exits from the envelope.

One especially attractive utilization of the inventive process takesadvantage of the fact that such an image intensifier normally isprovided with two tubulations in the end of the envelope thataccommodates the viewin screen. Providing a third such tubulationpermits the tines of a three-tine fixture to be easily inserted intotheprincipal envelope piece for advancement into coupling engagementwitha pickup packtemporarily held. near the sealing land of the envelopepiece at the start of the sealing process. With the pack thus engaged bythe fixture, the fixture may be retracted to displace the pickup packaway from the area where the seal is to take place, protecting it fromthe adverse influence of the sealing temperature. After the seal hasbeen completed, the fixture may be advanced once again, positioning thepickup pack with its mounting provisions aligned with the aperturesprovided in the sealing land of the envelope. After mounting pins areinserted to lock the pickup pack in this position, the fixture may bewithdrawn and the processing of the tube continued in conventionalfashion.

Brief description of the drawing The features of the present inventionwhich are believed to be novel are setforth with particularity in theappended claims. The invention, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription taken in connection with the accompanying drawings, in theseveral figures 'of which like reference numerals identify likeelements, and in which:

FIG. 1 is a view partially in cross section illustrating one of theassembly steps for the manufacture of an image intensifier;

FIG. 2 is an exploded view showing the details of the anode subassembly;

FIG. 3 is a fragmentary sectional view illustrating another manipulativestep in the process of manufacture; and

FIG. 4 is a fragmentary sectional view to show the anode subassemblyinstalled within the image intensifier.

Description of the preferred embodiment It is convenient first todescribe the structure of the improved image intensifier and then theprocess by which i it may be manufactured. The envelope is formed ofglass be described hereafter. At its opposite end envelope section has asealing land 11 which accommodates a plurality of apertures 12. Threesuch apertures have been shown and are spaced 120 apart. As seen mostclearly in FIG. 3, a ferrule 13 is inserted in each aperture and issealed to envelope section 10. Each ferrule has a centrally locatedaperture or channel through which a mounting pin may be inserted intothe envelope. The envelope is completed bya glass cap section 14 whichhas the same dimension and configuration as sealing land 11 of envelopesection 12. They are sealed together in any well-known manner foreffecting a glass to glass vacuumtight seal.

Within the envelope there is a transverse component i which for thestructure under consideration is the usual pickup pack 22, a fragmentarycross sectional view of 4 which is shown in FIG. 3. The pickup pack hasa ringshaped frame 21, assuming, of course, that the envelope 10 iscylindrical in cross section. The ring is formed of a U-shapedstructural element having a horizontal flange 21a adjacent sealing land11 and having on the other side of the rim a canted flange 21b which isprovided with three apertures 21c likewise having an angular separationof The overall or maximum dimensions of frame 21 are less than theminimum internal dimensions of envelope 10 so that the pickup pack mayconveniently be inserted into and supported transversely of envelope 10.To support the pickup pack in position there are a plurality of mountingprovisions spaced about frame 21 in radial alignment with the aperturesof ferrules 13. As shown, a threaded bushing 22 is in alignment witheach ferrule (only one appears in the drawing). The pickup pack ismechanically secured in position by a series of mounting pins 23 whichindividually are inserted through the apertures of ferrules 13 so that athreaded termination thereof may be accepted by threaded bushing 22. Atthe opposite end where each pin projects exteriorly of the centralportion of ferrule '13, itis heliarc welded to the ferrule to complete avacuum-tight seal between each ferrule and its mounting pin.

Frame 21 supports a spherical or dish shaped element 24 serving as thesubstrate of a photocathode and, of course, it must be transparent tothe radiation to which the intensifier is to respond. For manyinstallations, particularly where X-radiation is to be received, thismember may be formed of thin aluminum. The photocathode is composed of afirst layer of an X-ray sensitive phosphor, such as silver activatedzinc sulphide or the like, embodied in a suitable silicone resin anddeposited on element 24. Superimposed on the phosphor layer is a barrierlayer which may be formed, for example, of aluminum oxide and placed ontop of the barrier is a photocathode layer which may be of conventionalcomposition such as antimony-cesium. It is necessary to establish thephotocathode structure at a desired operating potential which is usuallyground and this may be accomplished by utilizing one of pins 23 as aterminal connector.

The remainder of the electrical system of the intensifier includesfocusing electrodes, an anode and a phosphor viewing screen. Theelectrodes are in the form of conductive bands vapor deposited on theinner surface of envelope 10. Three such bands are shown; one designated25 contacts ferrules 13 and is at the same electrical potential as thecathode. A second band 26 is isolated from the first by an uncoated ringor envelope section therebetween. Its operating potential may beestablished by connections made to a terminal connector 27 sealed to theenvelope and in electrical contact with band 26. The final focuselectrode 28 is spaced and insulated from band 26 and has a similarterminal connector 29. It extends to midway of the shoulder portion ofenvelope 10. Finally, there is an anode subassembly centrally positionedwithin well 9 of envelope 10.

The components of this subassembly are shown in the exploded view ofFIG. 2 and comprise a viewing window 31 which is a circular disk of.optical flat glass on one surface of which is formed a clamping ring32;this ring surrounds and defines the viewingwindow 33. Disk 31 isfused to the central portion of envelope section 9.

The next component of the subassembly is a glass disk 35 which bears onone surface a fluorescent coating to respond to impinging electrons anddevelop a light image to be viewed through window 33.Disk 35 is mountedin mately 120 from one another. The various components of phosphorscreen 35 and its mount are dimensioned to be received within theenlarged end of an anode electrode having a small diameter cylindricalsection 40 which faces pickup pack 2 0 and a conical section 41, thelarge end of which receives fluorescent screen 35 with its mount. It ispreferred to cut away the final portion of conical section 41 for adepth corresponding essentially to the height of screen 35 and itsmount. Where this is done, an angular rim 42 is presented against whichsprings 38 may bear to urge section 35 forwardly against viewing window33 when the subassembly is installed. To facilitate the installation thecutaway final portion of the anode terminates in a ring 43 and has aseries of longitudinally extending slots 44 which permit this section tobe resilient. The inner diameter of ring 43 is slightly less than themaximum diameter of ring 32 constructed on disk 31. To install thesubassembly fluorescent screen 35 with its mount is positioned withinanode 40 and the anode is then positioned concentrically over ring 32and advanced forward. The flexibility of the terminal portion of theanode permits ring 43 to slide over and lock beneath ring 32 of disk 31,installing subassembly 30 as shown in FIGS. 1 and 4. An anode terminalconnector 45 connects with conical section 41 and is available toconnect with a power supply through a tubulation 46. The supportingframe of screen 35 is of conductive material so that the anode potentialextends to the screen. The surface of well 9 extending from the outerperiphery of anode subassembly Q to the shoulder of the envelope iscovered with a deposit of conductive metal such as chrome or aluminium.Between this conductive coating and electrode 28, there is a coating 47of high resistance material such as chrome oxide. This coating extendsbetween both conductive coatings and establishes a desired potentialgradient therebetween but, more importantly, precludes the establishingof electrostatic charges on the shoulder of the envelope.

Finally, the image intensifier when completed has a pair of tubulations50 and 51. These are attached to the closure portion of envelope section10 and are spaced closer to the axis of the envelope than apertures 12of sealing land 11. One, of course, is supplied for purposes ofexhausting the envelope and it is sealed when the exhaust step has beencompleted. The other permits the attachment of an appendage or ion pumpthat is frequently employed with image intensifiers to preserve thevacuum condition throughout its operation. This ion pump whichconstitutes no part of the present invention has not been shown.

In the operation of the described image intensifier, operatingpotentials from a suitable and conventional power supply (not shown) areapplied to focusing electrode terminals 27 and 29 as well as to anodelead-in 45 while the photocathode is established at ground potential. Animage of X-radiation is focused through cap 14 of the envelope ontopickup pack a. It is converted into a light image at the phosphor layerof the photocathode which excites the photocathode layer giving rise toan electron image. That image is accelerated in the direction of theanode and focused through anode cylinder 40 upon fluorescent screen 35.The screen, in response to the electron image, produces another andintensified light image which is viewed through window 33. The operationof the image intensifier is, in all respects, conventional.

In the manufacture of the described structure, the glass disk 31 withits formed ring 32 is sealed centrally of well 9 of the envelope.Thereafter, a deposit of chromium is made on the shoulder of theenvelope and is baked for approximately one half hour at approximately425 to be converted into chrome oxide. This coating is the highresistance layer 47 of FIG. 1 and is most resistant to scratching. It isalso resistant to acids that may be used in washing or processing theenvelope. After chrome oxide layer 47 has been formed, it is covered ormasked as are the other portions of envelope section 10 that are to beleft free of a conductive deposit. Chromium or aluminum is now depositedby evaporation on the exposed portions of envelope 10 which providesbands 25, 26, 28 as well as the conductive coating that is to extendfrom shoulder 9 to anode subassembly 3 0. Having formed these conductivedeposits, the anode subassembly Q is installed in position by forcing acoupling engagement of ring 43 of anode section 41 with ring 32 of disk31. Thereafter anode lead 45 is inserted through tubing 46 and isattached.

The envelope is now supported in a vertical lathe, assuming the positionrepresented in FIG. 1. At this time, the envelope has both tubulations50, 51 and it also has a third tubulation 52, the three being angularlyspaced by 120 and being in alignment with although closer to the axisthan apertures 12 of envelope 10. More specifically, a plane includingthe tube axis also includes one of apertures 12 and one of tubulations52 which is one convenient geometrical arrangement to facilitateattaining the necessary radial alignment of bushings 22 with ferrules 13even though the screen pack is brought to its final position after theintensifier envelope shall have been completed. At this point, a fixturehaving three tines 61 is positioned so that its tines enter tubulations5052, respectively. The fixture is advanced toward well 9 of theenvelope and the lengths of the tines are such that with the fixturethus advanced, the apertures 21c provided in frame 21 of pickup pack 29may receive reduced diameter portions 63 of the tines as illustrated inFIG. 3. If bushings 22 are in alignment with aperture 21c, respectively,the fixture {31); is advanced until time sections 63 pass throughapertures 21c and abut against bushings 22 which serve as stops. Thiscompletes a coupling engagement of fixture 60 with the pickup frame andas the fixture is now withdrawn or moved axially away from envelope 10,pickup pack is displaced away from sealing land 11 in the direction ofanode subassembly 3Q. With pickup pack 20 in the position indicated inFIG. 1, cap 14 is sealed to land 11 of envelope section 10 and duringthis sealing process nitrogen or other inert gas is admitted from asupply 65 through the components of fixture 60 which are formed oftubing or channeled components to establish a suitable distribution fromsupply 65 to lines 61. Each tine has an exhaust port 66 that is locatedwithin envelope section 10 at this time and the flushing with thenitrogen or argon produces an air flow directed away from pickup pack E.This not only cools the plate, as desired to protect it from heat damageduring the sealing of the envelope pieces, but also flushes the pickuppack and tends to prevent contaminants from coming to rest on the pickuppack.

After cap -14 has been sealed and the structure permitted to cool, thenitrogen supply is cut off and fixture 60 is advanced once again toelevate pickup pack 2Q and position mounting bushings 22 in radialalignment with the apertures of ferrules 13. Mounting pins 23 are theninstalled, one end threaded into bushing 22 and the other heliarc Weldedto ferrule 13. Of course, if pins 23 have excessive length, it isappropriate to cut the ends that would otherwise project beyond ferrules13. With pickup pack Q secured in position, fixture 60 is withdrawncompletely and one of the tubulations 5052 is sealed off, leaving theother two to accommodate the exhaust and the 10m pump.

At this juncture, the processing of the tube insofar as assembling thestructure is concerned will have been completed except for theestablishment of the photocathode layer of pickup section 2;() which, asinstalled initially, is only equipped with its phosphor and barrierlayers. The photocathode layer is put down by evaporation or other wellknown techniques in a process that is thoroughly understood in the artand need not be described herein. Thereafter, the appendage pump isafiixed to one tubulation 50 or 51 and the intensifier is evacuated andsealed off; again by process steps well known to the art.

The described structure has very distinct advantages over predecessordevices, both as to ease of manufacture and reduction in cost. It is amore suitable structure from the standpoint of mass production and has aminimum of metallic components integrated into the envelope. The

arrangement of phosphor screen 35 within anode section 41 prevents lightfeedback from the viewing screen pickup pack E which is highlydesirable.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in' the art that changesand modifications may be made without departing from the invention inits broader aspects, and, therefore, the aim in the appended claims isto cover all suchchanges and modifications as fall within the truespirit and scope of the invention.

I claim:

1. In the manufacture of an image intensifier comprised of a multipiecesealed envelope having a plurality of apertures spaced about the sealingend of one of said internal dimensions of said one envelope piece andhaving a like plurality of mounting provisions spaced on the peripherythereof in the same angular orientation as that of said plurality of.apertures, a method of assembling which comprises:

inserting said component in said one envelope piece but displaced fromsaid plurality of apertures thereof in the direction of said oppositeend;

sealing a second envelope piece to said sealing end of said one envelopepiece;

advancing said component toward the seal between said envelope pieces toposition said mounting provisions thereof in radial alignment with saidplurality of apertures;

inserting mounting pins through said plurality of apertures intocoupling engagement with said mounting provisions of said component;

and making a vacuum-tight seal between each of said mounting pins andsaid one envelope piece.

2. The method of assembling an image intensifier in accordance withclaim 1 in which one tine of a fixture is inserted through each apertureof said closing envelope section into coupling engagement with saidcomponent and in which said fixture is moved in the direction of saidsealing-end to advance said component and position said mountingprovisions thereof relative to said plurality of apertures.

3. A method of assembling an image intensifier in accordance with claim2 in which said component is inii tially positioned. within said oneenvelope piece in the vicinity of said sealing end and in which saidtines of said fixture are brought into coupling engagement with saidcomponent while it is inits initial position and in which said fixtureis then withdrawn to displace said component from said plurality ofapertures in the direction of said closing envelope section prior to thesealing of said envelope sections.

4. A method of assembling an image intensifier in accordance with claim3 in which said one envelope section is supported in a vertical positionwith said sealing end thereof facing upward and in which the couplingengagement of the tines of said fixture with said component is effectedby gravity.

5. A method of assembling an image intensifier in accordance with claim4 in which said component has a peripheral rim with a flange portionfacing said closing envelope sectionand having recesses corresponding innumber and angular orientation to said apertures of said closingenvelope section and into [which said tines are inserted to effect acoupling engagement with said comsaid one envelope piece when saidfixture is in engagement with said component and in which an inert gasis admitted into said one envelope piece through said tubing to createan inert atmosphere for the sealing of said envelope pieces.

7. A method of assembling animage intensifier in accordance with claim 2in which a tubulation extends from each of said apertures of saidclosing end section and in which said tines are inserted through saidtubulations.

8. A method of assembling an image intensifier in accordance with claim1 in which electrodes, individually comprising a conductive coating, areapplied to spaced portions of the inner periphery of said one envelopepiece in the area thereof between said plurality of apertures and saidclosing end section prior to the insertion of said component into saidone envelope piece.

9. A method of assembling an image intensifier in accordance with claim8 in which an anode subassembly is aflixed to the central portion ofsaid closing envelope section prior to the application of said focusingelectrode and in which said component comprises a photocathode theinstallation of which completes an electrode system for saidintensifier.

10. In the manufacture of an image intensifier comprised of a multipiecesealed envelope having a plurality of apertures spaced about the sealingend of one of said envelope pieces, having a plurality of tubulationsextending from the opposite end of said one piece but spaced closer tothe axis of said envelopethan said apertures and further comprised of aphotocathode having maximum dimensions less than the internal dimensionsof said one envelope piece and having a like plurality of mountingprovisions spaced on the periphery thereof in the same angularorientation as that of said apertures, a method of assembling whichcomprises:

supporting said one envelope piece in position for sealing with anotherenvelope piece;

inserting said photocathode in the sealing end of said one envelopepiece with the mounting provisions thereof in the same angularorientation as said apertures;

inserting in each of said tubulations one tine of a supporting fixtureand advancing said fixture in the direction of said sealing end intocoupling engagement with said photocathode;

withdrawing said fixture to displace said photocathode from saidapertures in the direction of said opposite end of said one envelopepiece;

sealing said one envelope piece. to another envelope piece;

advancing said fixture to position said mounting provisions of saidphotocathode inradial alignment with said plurality of apertures;

inserting mounting pins through said apertures and into couplingengagement with said mounting provisions of said photocathode;

and making a vacuum-tight seal between each of said mounting pins andsaid one envelope piece.

References Cited UNITED STATES PATENTS 2,647,298 8/ 1953 Pryslar et al2925.15 2,792,273 5/1957 Beggs 31620 3,026,163 3/ 1962 Day 3l6213,366,435 1/1968 Lafferty 3l6-24 3,465,401 9/ 1969 Lowery, Jr., et a1.29--25.16

JOHN F. CAMPBELL, Primary Examiner R. I. CRAIG, Assistant Examiner U.S.Cl. X.R.

